CA1139079A - Pocess for the purification of phosphogypsum - Google Patents
Pocess for the purification of phosphogypsumInfo
- Publication number
- CA1139079A CA1139079A CA000343649A CA343649A CA1139079A CA 1139079 A CA1139079 A CA 1139079A CA 000343649 A CA000343649 A CA 000343649A CA 343649 A CA343649 A CA 343649A CA 1139079 A CA1139079 A CA 1139079A
- Authority
- CA
- Canada
- Prior art keywords
- phosphogypsum
- ozone
- equal
- suspension
- weight
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/46—Sulfates
- C01F11/468—Purification of calcium sulfates
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Inorganic Chemistry (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process for purifying phosphogypsum by treating it in an aqueous medium with ozone, the ozone being used being equal to at least 150 parts per million by weight of the phospho-gypsum, calculated as CaSO4.2H2O. Attempts to whiten phospho-gypsum using a bleaching agent have been generally unsuccessful under industrial conditions, with handling and pollution problems being most difficult to solve. By the present process white phosphogypsum is obtained, with the foregoing problems being alleviated.
A process for purifying phosphogypsum by treating it in an aqueous medium with ozone, the ozone being used being equal to at least 150 parts per million by weight of the phospho-gypsum, calculated as CaSO4.2H2O. Attempts to whiten phospho-gypsum using a bleaching agent have been generally unsuccessful under industrial conditions, with handling and pollution problems being most difficult to solve. By the present process white phosphogypsum is obtained, with the foregoing problems being alleviated.
Description
The present invention relates to a process ~or the purification of synthetic yypsum obtained by reac-tlng phosphate xocks with sulfuric acid. More specially it relates to a process for treatment o~ synthetic gypsum with ozone.
The commercial production of phosphoric acid by reacting sulfuric acid with phosphate rocks results in the formation of gypsum having the formula CaSO4.2H20. The so obtained gypsum, generally called phosphogypsum, is still colored, even after a purification treatment by washing with wa-te.r. Therefore it is not possible to use phosphogypsum as a filler, in particular in the paper industry.
In the latter industry, fillers, used as mass fillers, must have a whiteness grade measured according to French Standard NF Q 030303 higher than 75 and fillers used as coating fillers must have a whiteness degree higher than 86.
After washing with water, phosphogypsum has a whiteness grade only in the range of 63 to 70 depending on the -treated phosphate rock.
According to the present invention a phosphogypsum having a whiteness grade higher than 75 is obtained, despite the initial colour of the treated phosphogypsum.
In order -to obtain white phosphogypsum attempts were made to treat phosphogypsum by a bleaching agent usually used, for instance, in treating cellulosic fibers. Unfortunately, th.e treatment with bleaching agents, such as sodium hypochlorite, calcium hypochlorite, chlorine dioxide, hydrogen peroxide and sodium bisulfite, cannot be carried out under industrial conditions. Moreover, in using these bleaching agents handling and pollution problems which result therefrom are difficult to solve.
~ he present inven-tion relates to a process for improving ~he whiteness grade of phosphogypsum according to which the phospho-gypsum is treated by weak amounts of ozone.
Fur-thermore, the present invention relates to a purification process for phosphogypsum characterized in that a phosphogypsum suspension in an aqueous medium is treated with ozone. According to -the process of the invention, phosphogypsum produced by reacting phosphate rock wi-th sulfuric acid is filteredr preferably washed with wa-ter and placed in suspension in water, the maximum concentration o~
phosphogypsum being at most 70 percent by weigh-t and preferably ranging from 30 to 50 percent by weight. For concentrations higher than 70 percent by weight the suspension cannot be handled.
The invention consists in a process for purification of phosphogypsum characterized in that a phosphogypsum suspension in an aqueous medium is treated with ozone, using an amount of ozone equal to at least 150 parts per million by weight of phosphogypsum calculated as CaSO4.2H20.
After washing by water the phosphogypsums have a whiteness grade reaching at most 70. To increase this whiteness grade up to a valve equal to 76 it is sufficient according to the presen-t invention to treat phosphogypsum with a quantity oE ozone equal to 150 parts per million by weight based on the phosphog~psum.
The purification process of the present invention is characterized in that phosphogypsum, placed in suspension in an aqueous medium, is -treated by ozone by using an amount of ozone equal to at least 150 ppm (parts per millions) by weight relative to the CaSO4.2H20.
This minimal amount corresponds to the.ozone amount which is actually used in the reaction medium. This amount can be different from the whole amount introduced into the reaction medium~ Thus, par-t of the ozone introduced into the reaction medium can escape, the amount depending on the reaction yield, which depends on the apparatus used. In practice, the minimal amount of oæone which has to be used is the difference be-tween ~ 3~
the ozone amount which is introduced into the apparatus and the ozone amount which escapes from the apparatus. When an apparatus having a yield equal to 100 percent is used the minimal amount of ozone which is used is equal to ~he ozone amount which is actually introduced.
I-t is possible to grind the phosphogypsum suspension before treatment with ozone. It is also possible to grind the phosphogypsum ~hich has been obtained after ozone treatment.
The grinding step performed before or after treatment with ozone is essential when phosphogypsum is used as a filler for the coating of paper. For this application it is necessary that its degree of fineness is greater than when it is used as a filler in the mass.
The ozone used for the process of the present invention is o~tained as a gaseous dilute mi~ture by introducing a gaseous current containing oxygen in-to an ozone apparatus which transforms at least part of the oxygen into ozone. Electric discharges can be used, for lnstance, to achieve this reac-tion.
The ozone apparatus provides a gaseous current which is either a mixture constituted by oxygen, azote and ozone (obtained for instance by ozonizing air) or a mixture constituted by oxygen and ozone.
The amount of ozone in the gas provided by the ozone apparatus is generally in the range of 2 to 10 grammes per loa liters of gas.
The process of the present invention is achieved at any temperature which allows phosphogypsum to be kept in the form of a suspension in water, this temperature being higher than the freezing point and lower than the boiling point of the aqueous phase and it is preferably between 0 and 50~ and particularly at room temperature.
Preferably the process of the presen-t inverltion is carried out under atmospheric pressure, althouyh i-t is also possible to perform the process a~ higher pressures.
The pH of -the aqueous phase in which phosphogypsum is in suspension has any value bu-t the resul-ts ob-tained are improved when the aqueous phase is acid and preferably has a pH lower than or equal to 3. Thus, it is not necessary to neutralize aqueous suspensions of ph.osphogypsum which still contain minor amounts o~ sulfuric and phosphoric acids.
The process of the present invention is achieved in a continuous or discontLnuous wAy. The reactors used are thosè
suitable for the absorption of a gas into a liquid. When the process is achieved in a continuous manner the gas and suspension are countercurrently or co-currently introduced.
As noted hereabove, the phosphogypsum obtained according to the process of the present invention is suitable as a filler in the paper industry after filtration, drying and possibly a grinding step.
The phosphogypsum ~reated by ozone can also be used for the preparation of plaster CaSO4~1/2 H20 and more particularly for the prepara-tion of hemi-hydrate.
I-t is to be noted that the treatrnent of phosphogypsum by ozone has a surprising effect on this use.
It is known that plasters (hemi-hydrate ~; CaSO~..1/2 H20) prepared by calcination of a phosphogypsum purified only by washing with wa-ter are subject on the surface of materials mixed with water to the formation and development of moulds~
In order to avoid this drawback, it is known to add fungicides to the plaster before mixing with water.
It has been found that plas-ter (hemi-hydrate ~, CaSO4.1/2 H20~ obtained by calcining phosphogypsum treated by ozone according to the process of the present invention and mixed wi-th water (particularly plaster board) has much l.ess tendency to be subject to the formatiorl of mould and mould formation is even ~uite avoided when the whiteness grade of phosphogypsum reaches 82.
Thus, the purifica-tion process of the present invention provides plasters which do not need a large amount of fungicide and if the phosphogypsum used has a whiteness grade at least equal to 82 no addition of fungicide is needed.
The following examples are given by way of explanatory illustration.
Example 1 In a cylindrical reaction vessel (volume 10 liters, height : 70 cm) provided with a stirrer, 12 kg of an aqueous suspension containing 30 percent by weight of phosphogypsum having a whiteness grade equal to 64 were introduced. The suspension was at room temperature and it had a pH equal to 3.
The reaction vessel was stirred and oxygen coming from an ozone apparatus and containing 5 g of ozone per 100 litres of gas was introduced into the bottom of the reaction vessel. The gaseous flow was equal to 100 liters/hour.
The reaction was stopped after one hour. The difference between the amount of ozone which was introduced to the reaction vessel and the amount of ozone which leaked out of the reac-tion vessel was equal to 600 ppm (parts by weight per million~ based on phosphogypsum contained ln suspension. After filtration and drying, phosphogypsum having a whiteness grade equal to 77 was obtained.
Comparative example (example 1 bis) Example 1 was repeated by treating 2 ~y of the same aqueous suspension of phosphoqypsum (30 percen-t by weight and whiteness grade equal -to 64) with 18g of hydrogen peroxide at 110 volumes.
The reaction mixture was stirred for 3 hours a-t 20C at normal pressure and then a part of the suspension was filtered and dried. The -trcated phosphogypsurn had a whiteness grade equal -to 69.
The reaction medium which was no-t -trea-ted was stirred again for two hours. After treatmen-t the phosphogypsum obtained had a whiteness grade equal to 69~S.
Example 2 Into the same reaction vessel as in example 1, through the bottom of the reactor, an aqueous suspension (pH = 3~
containing 50 percent by weight of phosphogypsum having a whiteness grade equal to 70 was introduced. The temperature of the reaction medium was 20C. The f:Low of the aqueous suspension was equal to 19 kg/hour and the co-current gaseous flow coming from the apparatus and obtained by introducing an air current from an ozone apparatus was equal to 100 l/h; it contained 3.3 g of ozone per 100 liters.
When the flow became steady the suspension which flowed by way of overflow from the reactor vessel was filtexed. The phosphogypsum obtained was dried and it had a whiteness grade equal.to 180 parts per million based on the weight of phosphogypsum.
Example 3 Example 2 was repeated excep-t that a phosphogypsum having an initial whiteness grade equa]. to.65 was treated. By using 500 parts per million of ozone based on the weight of phosphogypsum, a whiteness grade equal to 77 was obtained in the product.
- Example 4 Example 3 was repeated except that a phosphogypsum suspension having a pH equal to 11 and a whiteness grade of phosphogypsum equal to 65 was used. By using 700 parts per million of ozone based on the weight of phosphogypsum, a 30 whiteness grade equal to 76 was obtalned in the p.roduct.
Example 5 Example 3 was repeated except that the temperature of the reaction medium was equal to 40C instead of 20~C. 700 parts 7~
per million of ozone were necessary -to raise the whi-teness grade of phosphoyypsum f~om 65 to 76.
Example 6 Example 2 was repeated (p~ = 3, temperature = 2QC) by using a phosphogypsum having a whiteness grade equal to 61.
By using 870 parts per million oE ozone based on the weight of phosphogypsum a phosphogypsum having a whiteness grade equal to 76 was obtained.
Exam Example 3 was repeated. By using 1,300 parts per million of o~one phosphogypsum was obtained which had a whiteness grade of 82.
Example 8 The phosphogypsum obtained in example 7 had the following particle size:
100% smaller than 150 microns with 7% smaller than 10 microns.
The phosphogypsum was ground so that 100% of the particles were smaller than 10 microns. The whi-teness grade of the ground phosphog~psum was e~1ual to ~7.
Example 9 The phosphogypsum obtained in example 3 was calcined, in order to obtain plaster ~hemi-hydrate ~, CaSO4O1/2 H~0). This plaster was used to manufacture a board. The board obtained had a surface where the formation of mould was decreased in comparison wikh board stacked under the same conditions and manufactured with plaster obtained from phospho~ypsum which was not treated according to the process of the present invention.
Example 10 The phosphogypsum obtained in example 7 was calcined in order to obtain plaster and the plaster was used -to ma~e a board.
As with example 9, -the board obtained had a surace on which mould was avoided.
The commercial production of phosphoric acid by reacting sulfuric acid with phosphate rocks results in the formation of gypsum having the formula CaSO4.2H20. The so obtained gypsum, generally called phosphogypsum, is still colored, even after a purification treatment by washing with wa-te.r. Therefore it is not possible to use phosphogypsum as a filler, in particular in the paper industry.
In the latter industry, fillers, used as mass fillers, must have a whiteness grade measured according to French Standard NF Q 030303 higher than 75 and fillers used as coating fillers must have a whiteness degree higher than 86.
After washing with water, phosphogypsum has a whiteness grade only in the range of 63 to 70 depending on the -treated phosphate rock.
According to the present invention a phosphogypsum having a whiteness grade higher than 75 is obtained, despite the initial colour of the treated phosphogypsum.
In order -to obtain white phosphogypsum attempts were made to treat phosphogypsum by a bleaching agent usually used, for instance, in treating cellulosic fibers. Unfortunately, th.e treatment with bleaching agents, such as sodium hypochlorite, calcium hypochlorite, chlorine dioxide, hydrogen peroxide and sodium bisulfite, cannot be carried out under industrial conditions. Moreover, in using these bleaching agents handling and pollution problems which result therefrom are difficult to solve.
~ he present inven-tion relates to a process for improving ~he whiteness grade of phosphogypsum according to which the phospho-gypsum is treated by weak amounts of ozone.
Fur-thermore, the present invention relates to a purification process for phosphogypsum characterized in that a phosphogypsum suspension in an aqueous medium is treated with ozone. According to -the process of the invention, phosphogypsum produced by reacting phosphate rock wi-th sulfuric acid is filteredr preferably washed with wa-ter and placed in suspension in water, the maximum concentration o~
phosphogypsum being at most 70 percent by weigh-t and preferably ranging from 30 to 50 percent by weight. For concentrations higher than 70 percent by weight the suspension cannot be handled.
The invention consists in a process for purification of phosphogypsum characterized in that a phosphogypsum suspension in an aqueous medium is treated with ozone, using an amount of ozone equal to at least 150 parts per million by weight of phosphogypsum calculated as CaSO4.2H20.
After washing by water the phosphogypsums have a whiteness grade reaching at most 70. To increase this whiteness grade up to a valve equal to 76 it is sufficient according to the presen-t invention to treat phosphogypsum with a quantity oE ozone equal to 150 parts per million by weight based on the phosphog~psum.
The purification process of the present invention is characterized in that phosphogypsum, placed in suspension in an aqueous medium, is -treated by ozone by using an amount of ozone equal to at least 150 ppm (parts per millions) by weight relative to the CaSO4.2H20.
This minimal amount corresponds to the.ozone amount which is actually used in the reaction medium. This amount can be different from the whole amount introduced into the reaction medium~ Thus, par-t of the ozone introduced into the reaction medium can escape, the amount depending on the reaction yield, which depends on the apparatus used. In practice, the minimal amount of oæone which has to be used is the difference be-tween ~ 3~
the ozone amount which is introduced into the apparatus and the ozone amount which escapes from the apparatus. When an apparatus having a yield equal to 100 percent is used the minimal amount of ozone which is used is equal to ~he ozone amount which is actually introduced.
I-t is possible to grind the phosphogypsum suspension before treatment with ozone. It is also possible to grind the phosphogypsum ~hich has been obtained after ozone treatment.
The grinding step performed before or after treatment with ozone is essential when phosphogypsum is used as a filler for the coating of paper. For this application it is necessary that its degree of fineness is greater than when it is used as a filler in the mass.
The ozone used for the process of the present invention is o~tained as a gaseous dilute mi~ture by introducing a gaseous current containing oxygen in-to an ozone apparatus which transforms at least part of the oxygen into ozone. Electric discharges can be used, for lnstance, to achieve this reac-tion.
The ozone apparatus provides a gaseous current which is either a mixture constituted by oxygen, azote and ozone (obtained for instance by ozonizing air) or a mixture constituted by oxygen and ozone.
The amount of ozone in the gas provided by the ozone apparatus is generally in the range of 2 to 10 grammes per loa liters of gas.
The process of the present invention is achieved at any temperature which allows phosphogypsum to be kept in the form of a suspension in water, this temperature being higher than the freezing point and lower than the boiling point of the aqueous phase and it is preferably between 0 and 50~ and particularly at room temperature.
Preferably the process of the presen-t inverltion is carried out under atmospheric pressure, althouyh i-t is also possible to perform the process a~ higher pressures.
The pH of -the aqueous phase in which phosphogypsum is in suspension has any value bu-t the resul-ts ob-tained are improved when the aqueous phase is acid and preferably has a pH lower than or equal to 3. Thus, it is not necessary to neutralize aqueous suspensions of ph.osphogypsum which still contain minor amounts o~ sulfuric and phosphoric acids.
The process of the present invention is achieved in a continuous or discontLnuous wAy. The reactors used are thosè
suitable for the absorption of a gas into a liquid. When the process is achieved in a continuous manner the gas and suspension are countercurrently or co-currently introduced.
As noted hereabove, the phosphogypsum obtained according to the process of the present invention is suitable as a filler in the paper industry after filtration, drying and possibly a grinding step.
The phosphogypsum ~reated by ozone can also be used for the preparation of plaster CaSO4~1/2 H20 and more particularly for the prepara-tion of hemi-hydrate.
I-t is to be noted that the treatrnent of phosphogypsum by ozone has a surprising effect on this use.
It is known that plasters (hemi-hydrate ~; CaSO~..1/2 H20) prepared by calcination of a phosphogypsum purified only by washing with wa-ter are subject on the surface of materials mixed with water to the formation and development of moulds~
In order to avoid this drawback, it is known to add fungicides to the plaster before mixing with water.
It has been found that plas-ter (hemi-hydrate ~, CaSO4.1/2 H20~ obtained by calcining phosphogypsum treated by ozone according to the process of the present invention and mixed wi-th water (particularly plaster board) has much l.ess tendency to be subject to the formatiorl of mould and mould formation is even ~uite avoided when the whiteness grade of phosphogypsum reaches 82.
Thus, the purifica-tion process of the present invention provides plasters which do not need a large amount of fungicide and if the phosphogypsum used has a whiteness grade at least equal to 82 no addition of fungicide is needed.
The following examples are given by way of explanatory illustration.
Example 1 In a cylindrical reaction vessel (volume 10 liters, height : 70 cm) provided with a stirrer, 12 kg of an aqueous suspension containing 30 percent by weight of phosphogypsum having a whiteness grade equal to 64 were introduced. The suspension was at room temperature and it had a pH equal to 3.
The reaction vessel was stirred and oxygen coming from an ozone apparatus and containing 5 g of ozone per 100 litres of gas was introduced into the bottom of the reaction vessel. The gaseous flow was equal to 100 liters/hour.
The reaction was stopped after one hour. The difference between the amount of ozone which was introduced to the reaction vessel and the amount of ozone which leaked out of the reac-tion vessel was equal to 600 ppm (parts by weight per million~ based on phosphogypsum contained ln suspension. After filtration and drying, phosphogypsum having a whiteness grade equal to 77 was obtained.
Comparative example (example 1 bis) Example 1 was repeated by treating 2 ~y of the same aqueous suspension of phosphoqypsum (30 percen-t by weight and whiteness grade equal -to 64) with 18g of hydrogen peroxide at 110 volumes.
The reaction mixture was stirred for 3 hours a-t 20C at normal pressure and then a part of the suspension was filtered and dried. The -trcated phosphogypsurn had a whiteness grade equal -to 69.
The reaction medium which was no-t -trea-ted was stirred again for two hours. After treatmen-t the phosphogypsum obtained had a whiteness grade equal to 69~S.
Example 2 Into the same reaction vessel as in example 1, through the bottom of the reactor, an aqueous suspension (pH = 3~
containing 50 percent by weight of phosphogypsum having a whiteness grade equal to 70 was introduced. The temperature of the reaction medium was 20C. The f:Low of the aqueous suspension was equal to 19 kg/hour and the co-current gaseous flow coming from the apparatus and obtained by introducing an air current from an ozone apparatus was equal to 100 l/h; it contained 3.3 g of ozone per 100 liters.
When the flow became steady the suspension which flowed by way of overflow from the reactor vessel was filtexed. The phosphogypsum obtained was dried and it had a whiteness grade equal.to 180 parts per million based on the weight of phosphogypsum.
Example 3 Example 2 was repeated excep-t that a phosphogypsum having an initial whiteness grade equa]. to.65 was treated. By using 500 parts per million of ozone based on the weight of phosphogypsum, a whiteness grade equal to 77 was obtained in the product.
- Example 4 Example 3 was repeated except that a phosphogypsum suspension having a pH equal to 11 and a whiteness grade of phosphogypsum equal to 65 was used. By using 700 parts per million of ozone based on the weight of phosphogypsum, a 30 whiteness grade equal to 76 was obtalned in the p.roduct.
Example 5 Example 3 was repeated except that the temperature of the reaction medium was equal to 40C instead of 20~C. 700 parts 7~
per million of ozone were necessary -to raise the whi-teness grade of phosphoyypsum f~om 65 to 76.
Example 6 Example 2 was repeated (p~ = 3, temperature = 2QC) by using a phosphogypsum having a whiteness grade equal to 61.
By using 870 parts per million oE ozone based on the weight of phosphogypsum a phosphogypsum having a whiteness grade equal to 76 was obtained.
Exam Example 3 was repeated. By using 1,300 parts per million of o~one phosphogypsum was obtained which had a whiteness grade of 82.
Example 8 The phosphogypsum obtained in example 7 had the following particle size:
100% smaller than 150 microns with 7% smaller than 10 microns.
The phosphogypsum was ground so that 100% of the particles were smaller than 10 microns. The whi-teness grade of the ground phosphog~psum was e~1ual to ~7.
Example 9 The phosphogypsum obtained in example 3 was calcined, in order to obtain plaster ~hemi-hydrate ~, CaSO4O1/2 H~0). This plaster was used to manufacture a board. The board obtained had a surface where the formation of mould was decreased in comparison wikh board stacked under the same conditions and manufactured with plaster obtained from phospho~ypsum which was not treated according to the process of the present invention.
Example 10 The phosphogypsum obtained in example 7 was calcined in order to obtain plaster and the plaster was used -to ma~e a board.
As with example 9, -the board obtained had a surace on which mould was avoided.
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for purification of phosphogypsum characterized in that a phosphogypsum suspension in an aqueous medium is treated with ozone, using an amount of ozone equal to at least 150 parts per million by weight of phosphogypsum calculated as CaSO4.2H2O.
2. Process according to claim 1 characterized in that the concentration of the suspension of phosphogypsum is at most 70 percent by weight.
3. Process according to claim 2 characterized in that the concentration of phosphogypsum in the suspension is 30 to 50 percent by weight.
4. Process according to any one of claims 1 to 3 characterized in that the ozone treatment is carried out at temperature between 0° and 50°C.
5. Process according to any one of claims 1 to 3 characterized in that the pH of the aqueous suspension is lower than or equal to 3.
6. Process according to any one of claims 1 to 3 characterized in that phosphogypsum is ground before treatment with ozone.
7. Process according to any one of claims 1 to 3 characterized in that phosphogypsum is ground after treatment with ozone.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7900772 | 1979-01-12 | ||
| FR7900772A FR2446256A1 (en) | 1979-01-12 | 1979-01-12 | CHEMICAL GYPSUM PURIFICATION PROCESS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1139079A true CA1139079A (en) | 1983-01-11 |
Family
ID=9220693
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000343649A Expired CA1139079A (en) | 1979-01-12 | 1980-01-11 | Pocess for the purification of phosphogypsum |
Country Status (19)
| Country | Link |
|---|---|
| US (1) | US4344925A (en) |
| AT (1) | AT368987B (en) |
| BE (1) | BE880952A (en) |
| BG (1) | BG39465A3 (en) |
| BR (1) | BR8000193A (en) |
| CA (1) | CA1139079A (en) |
| DE (1) | DE2952571A1 (en) |
| ES (1) | ES487650A1 (en) |
| FI (1) | FI66332C (en) |
| FR (1) | FR2446256A1 (en) |
| GB (1) | GB2039269B (en) |
| IN (1) | IN153514B (en) |
| IT (1) | IT1145402B (en) |
| MA (1) | MA18684A1 (en) |
| NL (1) | NL8000116A (en) |
| PL (1) | PL119292B1 (en) |
| PT (1) | PT70680A (en) |
| SE (2) | SE7910257L (en) |
| ZA (1) | ZA796744B (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4533528A (en) * | 1983-07-15 | 1985-08-06 | United States Gypsum Company | Process for continuously calcining gypsum to low dispersed consistency stucco |
| DE4242200C1 (en) * | 1992-12-15 | 1993-10-28 | Steag Ag | Process for improving the whiteness of raw gypsum |
| US6033468A (en) * | 1997-01-29 | 2000-03-07 | Folks; Timothy S. | Interground white blended cement |
| US6007620A (en) * | 1997-01-29 | 1999-12-28 | Folks; Timothy S. | Process to make interground, white, blended cement |
| CN102634843B (en) * | 2012-04-27 | 2015-04-22 | 昆明理工大学 | Method for preparing micron-sized calcium sulfate particles and crystal whiskers from phosphogypsum |
| CN103466577B (en) * | 2013-09-04 | 2016-01-20 | 贵州锦麟化工有限责任公司 | Improve the method for phosphoric acid by wet process quality |
| CN103496729B (en) * | 2013-09-04 | 2015-09-30 | 贵州锦麟化工有限责任公司 | Improve the method for by-product phosphogypsum quality in production process of phosphoric acid |
| CN115477485B (en) * | 2022-09-06 | 2023-08-22 | 常州大学 | Method for preparing alpha-hemihydrate gypsum by utilizing azo dye sulfuric acid wastewater |
| CN115504499A (en) * | 2022-10-21 | 2022-12-23 | 广州市勃发环境科技有限公司 | Method for refining gypsum from chemical wastewater containing sulfuric acid and sulfate |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA802105A (en) * | 1968-12-24 | Hayakawa Masashi | Process for preparing gypsum hemihydrate | |
| US1548358A (en) * | 1924-05-26 | 1925-08-04 | Rumford Chemical Works | Plaster of paris and method of making the same |
| GB339797A (en) * | 1928-12-18 | 1930-12-18 | Rene Perdu | |
| US2197003A (en) * | 1937-11-18 | 1940-04-16 | Glidden Co | Process for making pigments |
| DE1467470C2 (en) * | 1963-10-28 | 1974-06-12 | Pluess-Staufer Ag, Oftringen, Aargau (Schweiz) | Improvement of the whiteness of chalk, calcite or dolomite |
| US3616900A (en) * | 1969-07-09 | 1971-11-02 | Engelhard Min & Chem | Method for bleaching gray kaolin clay |
| US4113835A (en) * | 1972-07-06 | 1978-09-12 | Veba-Chemie Aktiengesellschaft | Process for preparing pure synthetic calcium sulfate semihydrate |
| FR2201682A5 (en) * | 1972-10-02 | 1974-04-26 | Cerphos | |
| GB1394910A (en) * | 1972-10-23 | 1975-05-21 | Pluss Stauffer Ag | Process for the optical brightening of minerals |
| SE417104B (en) * | 1978-10-30 | 1981-02-23 | Supra Ab | SET TO CLEAN RESPECTIVE PINK POLLUTANED CALCIUM SULPHATE INTENDED TO BE USED AS PIGMENT AND / OR FILLER |
-
1979
- 1979-01-12 FR FR7900772A patent/FR2446256A1/en active Granted
- 1979-12-12 SE SE7910257D patent/SE7910257L/en not_active Application Discontinuation
- 1979-12-12 GB GB7942864A patent/GB2039269B/en not_active Expired
- 1979-12-12 ZA ZA00796744A patent/ZA796744B/en unknown
- 1979-12-12 SE SE7910257A patent/SE434046B/en not_active IP Right Cessation
- 1979-12-21 IN IN935/DEL/79A patent/IN153514B/en unknown
- 1979-12-26 MA MA18886A patent/MA18684A1/en unknown
- 1979-12-28 DE DE19792952571 patent/DE2952571A1/en not_active Withdrawn
- 1979-12-28 BE BE0/198816A patent/BE880952A/en not_active IP Right Cessation
- 1979-12-31 AT AT0821379A patent/AT368987B/en not_active IP Right Cessation
-
1980
- 1980-01-07 FI FI800041A patent/FI66332C/en not_active IP Right Cessation
- 1980-01-07 BG BG8046178A patent/BG39465A3/en unknown
- 1980-01-08 NL NL8000116A patent/NL8000116A/en not_active Application Discontinuation
- 1980-01-10 PL PL1980221311A patent/PL119292B1/en unknown
- 1980-01-10 PT PT70680A patent/PT70680A/en unknown
- 1980-01-11 CA CA000343649A patent/CA1139079A/en not_active Expired
- 1980-01-11 ES ES487650A patent/ES487650A1/en not_active Expired
- 1980-01-11 IT IT47568/80A patent/IT1145402B/en active
- 1980-01-11 BR BR8000193A patent/BR8000193A/en unknown
-
1981
- 1981-01-15 US US06/225,232 patent/US4344925A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| ATA821379A (en) | 1982-04-15 |
| PL119292B1 (en) | 1981-12-31 |
| FI66332B (en) | 1984-06-29 |
| SE434046B (en) | 1984-07-02 |
| FI66332C (en) | 1984-10-10 |
| AT368987B (en) | 1982-11-25 |
| PL221311A1 (en) | 1980-10-06 |
| ES487650A1 (en) | 1980-06-16 |
| BR8000193A (en) | 1980-05-27 |
| DE2952571A1 (en) | 1980-07-24 |
| US4344925A (en) | 1982-08-17 |
| ZA796744B (en) | 1980-11-26 |
| BE880952A (en) | 1980-04-16 |
| IT1145402B (en) | 1986-11-05 |
| NL8000116A (en) | 1980-07-15 |
| PT70680A (en) | 1980-02-01 |
| FR2446256A1 (en) | 1980-08-08 |
| MA18684A1 (en) | 1980-07-01 |
| GB2039269B (en) | 1982-10-20 |
| BG39465A3 (en) | 1986-06-16 |
| IN153514B (en) | 1984-07-21 |
| SE7910257L (en) | 1980-07-13 |
| FR2446256B1 (en) | 1983-05-27 |
| FI800041A (en) | 1980-07-13 |
| GB2039269A (en) | 1980-08-06 |
| IT8047568A0 (en) | 1980-01-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |